Coal dissolving process

ABSTRACT

A process for dissolving sub-bituminous coal by heating said coal in the presence of a hydrogen donor oil, gaseous carbon monoxide, water, hydrogen, and an ammonium or alkali metal molybdate at a temperature of from about 400* to about 425*C and at a total pressure of from about 2000 to about 5000 psig.

United States Patent Seitzer et al.

[ Nov. 18, 1975 COAL DISSOLVING PROCESS Inventors: Walter H. Seitzer, West Chester;

Robert W. Shinn, Aston, both of Pa.

Sun Research and Development Co., Marcus Hook, Pa.

Filed: Jan. 15, 1973 Appl. No.: 323,568

Continuation-in-part of Ser. No. 250,999, May 8,

I972, abandoned.

Assignee:

US. Cl. 208/10 Int. Cl. Clog l/06 Field of Search 208/8, 10; 201/25 References Cited UNITED STATES PATENTS 7/1933 Harrison et al. 208/10 3,687,838 8/1972 Seitzer 208/10 FOREIGN PATENTS OR APPLICATIONS 102,303 10/1937 Australia 208/10 406,986 2/1934 United Kingdom..... 208/10 407,227 3/1934 United Kingdom 208/10 Primary ExaminerPaul M. Coughlan, Jr. Assistant ExaminerS. Berger Attorney, Agent, or Firm -George L. Church, Donald R. Johnson; Paul Lipsitz A process for dissolving sub-bituminous coal by heat-- ing said coal in the presence of a hydrogen donor oil,

ABSTRACT gaseous carbon monoxide, water, hydrogen, and an ammonium or alkali metal molybdate at a temperature of from about 400 to about 425C and at a total pressure of from about 2000 to about 5000 psig.

6 Claims, No Drawings COAL DISSOLVING PROCESS RELATED APPLICATION This application is a continuation-in-part of Ser. No. 250,999, filed May 8, 1972, and now abandoned.

Numerous coal liquefaction processes are well known in the art. For example, U.S. Pat. No. 2,686,152 discloses a lignitic coal extraction process carried out with an organic solvent such as Tetralin or a mixture thereof with a phenol at temperatures between about 480F (249C) and about 900F (460C) with or without hydrogen being used, and at atmospheric or at autogenous hydrogen pressure. This prior art disclosure indicates that liquid products are formed in an amount ranging from about 7% to about 50%. Such a procedure cannot economically lend itself toward commercial production of liquid products, since what is needed in any commercial coal liquefaction process is essentially complete liquefaction of the coal.

It is also known, as reported in Table 18 in chapter 22 of Chemistry of Coal Utilization, edited by H. H. Lowry (John Wiley and Sons, 1963) that bituminous coal may be liquified by hydrogenating its slurry at 460C in a pasting oil using various catalysts such as nickel, molybdenum, iron, and tin. Although the degree of solubilization reported is quite high, such processes have the severe disadvantage of requiring large volumes of expensive hydrogen and require temperatures above 450C for significant solubilization to occur.

Recently, as disclosed in U.S. Pat. No. 3,594,304 (Seitzer and Shinn, assigned to Sun Oil Co., issued July 20, 1971) a coal liquefaction process for sub-bituminous coal has been found which is able to achieve solution of 90% or more of the coal. This is accomplished by subjecting a sub-bituminous coal to solution in a hydrogen donor solvent under pressure of hydrogen of from about 2000 to about 3000 psig and maintaining the temperature of the process within the narrow range 440 to 450C for a period of about to about minutes residence time. This process is a significant improvement over previously available processes, but it does have an economic liability in that it requires the pressure of hydrogen used in the system to be rather high (2000 to 3000 psig) in order to achieve high dissolution of coal.

It is also known to convert sub-bituminous coal to benzene-soluble and volatile materials by use of a carbon monoxide and water atmosphere, but relatively low conversions are obtained by this technique. Thus, Appell and Wender (Reprints, Am. Chem. Soc., Div. of Fuel Chem., 156 Nat. Meeting, Sept. 1968; v. 12, no. 3, pp. 220-224) report that at 375C and short contact times, a conversion of 43% of sub-bituminous coal to benzenesoluble and volatile materials was obtained with carbon monoxide and water at a pressure of 4200 psig. With hydrogen at 5700 psig, the conversion was 27%. At 425C the difference in conversion decreased, but still favored the carbon monoxide-water by a significant margin.

In our application Ser. No. 181,229, filed Sept. 16, 1971, now U.S. Pat. No. 3,819,506, we disclosed that a high degree of sub-bituminous coal dissolution can be achieved without the previously required high hydrogen pressures, and even at somewhat lower temperatures than that of U.S. Pat. No. 3,594,304 referred to above, if the process is'carried out in a gaseous atmosphere of hydrogen (at relatively low pressure), carbon monoxide, and water by employing a hydrogenated anthracene oil. The process of that invention comprises dissolving sub-bituminous coal by heating a slurry of said coal in a solvent of anthracene oil especially bydrogenated to contain from about 7% to about 9% hydrogen, in the presence of carbon monoxide, hydrogen, and water, at about 400 to about 425C and at a total pressure of from about 2000 to about 5000- psig. Although that process represents a significant improve ment in the art in that a lower hydrogen pressure is required, any coal dissolution plant using the process still requires both a hydrogen plant and a solvent hydrogenator and such capital investment will add to overall cost.

It has now been found that sub-bituminous coal may readily be essentially completely solubilized by an economical highly efficient process using a solvent which need not be especially hydrogenated. This is accomplished by hydrogenating sub-bituminous coal in the presence of a donor solvent oil, carbon monoxide, water, and an alkali metal or ammonium molybdate at an elevated temperature of about 400 to about 425C and at a total pressure of about 2000 to about 5000 psig. It appears that the molybdate present acts as a catalyst to effect liquefaction without use of the especially hydrogenated solvent. Furthermore, the pressure of hydrogen is relatively low since the total pressure in the system is the sum of the pressures of steam, carbon monoxide, and hydrogen, which will be about equal at operating temperature. In this way the coal is essentially completely solubilized at relatively low hydrogen pressure and the liquid which is obtained is readily handled and subjected to normal refinery operations to provide useful liquid fuels.

As indicated, the coal used in the process of the invention will be a sub-bituminous coal and this will include lignite coals such as North Dakota lignite, Wyodak, Big Horn, Powder River Sub-Bituminous Coal, and the like.

The oil used in the process of the invention is a hydrogen donor solvent. These donor solvent materials are well known and comprise aromatic hydrocarbons which are partially hydrogenated, generally having one or more of the nuclei at least partially saturated. Several examples of such materials are tetralin, dihydronaphthalene, dihydroalkylnaphthalenes, dihydrophenanthrene, dihydroanthracene, dihydrochrysenes, tetrahydrochrysenes, tetrahydropyrenes, tetrahydrofluoranthenes and the like. Of particular value in the process of this invention as hydrogen donor solvents are the hydrophenanthrenes and hydroanthracenes such as dihydroanthracene. It will be understood that these materials may be obtained from any source, but are readily available from coal processing systems as anthracene oil, and the like. Of particular value are recycle oils from the coal dissolving process of the invention.

The molybdate salts which promote solution of the coal will preferably be an alkali metal (e.g., sodium, potassium, lithium, etc.) or an ammonium salt of molybdic acid; e.g., (NH )6Mo O .4I-I O. The amount of molybdate salt used in the process may vary over a wide range, but the usual amount will be from about 0.5 to about 10% by weight of the coal used, preferably from about 1 to about 7%.

It is significant to note that other metal salts, even though some are known to promote solubility in coal hydrogenations, are not operable in the process of this invention. For example, iron, cobalt, chromium and tin salts are ineffective in enabling high coal solubility to be obtained.

In one technique for carrying out the process of the invention a slurry of powdered sub-bituminous coal in the solvent is introduced into a pressure reactor. An amount of coal and solvent will generally be used such that the weight ratio of solvent to coal will be from about 1:1 to :1, preferably about 2:1. Although a higher ratio may be used, it may be uneconomical to do so. Then, if the water, carbon monoxide, and hydrogen are added as separate entities, water is placed in the reactor, and after closing it, it is pressured with carbon monoxide and with hydrogen. In pressuring the reactor, the partial pressure of hydrogen should not be greater than, and preferably less than, the partial pressure of carbon monoxide. In the process of the invention, both the hydrogen and the carbon monoxide make a contribution to the coal dissolution efficiency. Preferably, the partial pressure of hydrogen will be about the same as the carbon monoxide partial pressure. Likewise, the steam pressure generated from the water will preferably be equivalent to the hydrogen or carbon monoxide partial pressure. As the contents of the reactor are stirred or agitated, the temperature is raised rapidly to the temperature range of about 400 to about 425C and the total pressure rises to between about 2000 to about 5000 psig. The residence time for solution of the coal to occur is not critical and will usually be from about 0.5 to about 2 hours, preferably about 1 hour, during which time over 90% by weight of the coal will be brought into solution.

It is to be understood that the particle size of the coal used is not a critical parameter of the process. While it is preferred to use coal which has been comminuted, coarse particles and very large pieces will also be affected by the process and brought into solution. In fact, the process may even be carried out in subterranean coal mines, the seams of coalbeing solubilized by feeding the solvent with suspended molybdate promoter, carbon monoxide and steam into a closed underground cavern to build up heat and pressure as required by the process. The solubilized coal is then pumped from the cavern for use as later described.

In a preferred technique, the source of carbon monoxide, water, and hydrogen will be producer gas which is readily available from various sources in refinery operations. Producer gas is made by blowing a mixture of air or oxygen and steam through a bed of incandescent carbonaceous fuel and its compostion will vary depending upon the source of fuel and equipment used in making the gas (see Cost Engineering, July 1963, pages 4-l-l). Typically, producer gas from coke made with oxygen contains on a percent by volume basis about 53% CO and about 31% hydrogen and such a gas is quite useful. It will be understood that the composition of the producer gas used may be adjusted so as to provide the desired partial pressures of hydrogen and carbon monoxide in the pressure reactor used in subject invention, but with a gas such as described above, no such adjustment is necessary. Since producer gas may or may not contain water vapor, it may be adjusted to contain this component also, preferably in an amount such that the waterzCO molar ratio is from about 2:1 to 1:2, but, of course, water may be introduced into the reactor separately. The major advantage in using producer gas is that it provides an economical source of reactant carbon monoxide and hydrogen, and, furthermore, does not need to be refined for use in the process as the other components (CO H 8, NH CH and N do not interfere. Since the process of the invention is uniquely suited to use of producer gas, it is particularly valuable in providing an economical coal dissolving process.

The dissolved coal formed by the process of the invention is a valuable product similar in many respects to a crude oil and is subjected to the usual refining operations to produce petroleum products. For use in this manner, the solution is merely filtered to remove the small amount of insoluble products present, and the filtrate treated in accord with conventional refinery techniques.

In order to more fully describe the invention, the following examples are given:

EXAMPLE 1 A l-liter stirred autoclave is charged with 33 g of powdered Wyodak coal 20 mesh) and 67 g of anthracene oil and then 15 g of water containing 2.0 g of ammonium molybdate. The reactor is sealed, pressure tested, and then pressured with 600 psig of hydrogen and 600 psig of carbon monoxide. The reactor is heated to 415C for 1 hour, the total pressure reaching 3300 psig. The reactor is then allowed to cool, and the product then filtered to remove the solids which are washed with a toluene-acetone mixture, dried, and weighed. The percent of coal dissolved is 89%. When the above experiment is repeated, but without the ammonium molybdate, the amount of coal dissolved is only 57%.

When the above example is repeated with sodium molybdate, and using Big Horn Coal, essentially the same results are obtained.

EXAMPLE 2 Using the essential technique described above, several different metal salts are used in the system. The following table illustrates the results obtained:

TABLE I Percent Coal Metal Salt Dissolved Cr(NO;,) .9H O 54 MnCl .4H O 67 SnSO 62 CoCl .6H O 70 FeCl .4H O 64 It is clear from the table that these salts are all ineffective in the process.

EXAMPLE 3 I TABLE II Dissolution of-Wyodak Coal 33 gms Wyodak Coal. 67 gms Anthracene Oil, l5 ml H 0, 2 gms Ammonium Molybdate, 415C, l hr, Stirred Autoclave psig, Start Final Percent Coal H, CO psig Dissolvcd EXAMPLE 4 As in Example 1, a stirred autoclave is charged with 33 g of Wyodak Coal, 67 g of anthracene oil, and g of water containing 2 g of ammonium molybdate. Then to the sealed reactor, water free producer gas adjusted to contain equal volumes of hydrogen and carbon monoxide is pressured in to 1200 psig. After heating for 1 hour at 415C, the total pressure is 3400 psig. After cooling and separation of solids, 92% of the coal is found to have been dissolved.

{about 5000 psig, a mixture of said finely divided coal, a

The preceding experimental data indicates that the process of the invention provides a means for efficiently bringing coal into solution under economical conditions and thus the process provides a valuable contribution to the art of coal solubilization.

- The invention claimed is:

1. The process for dissolving sub-bituminous coal which comprises heating at about 400C. to about 425C. under a total pressure of from about 2000 to about 1% to about 7% hydrogen donor oil in a weight ratio to said coal of from about l :l to 5: 1, carbon monoxide, hydrogen in an amount such that its partial pressure is about the same as that of said carbon monoxide, water in an amount such that the molar ratio of water to carbon monoxide is from about 2:1 to 1:2, and as a promoter, an alkali metal or ammonium molybdate in an amount of from about 0.5 to about 10% by weight of said coal.

2. The process of claim 1 where the oil is anthracene oil and the promoter is an alkali metal molybdate.

3. The process of claim 1 where the oil is a recycle oil and the promoter is sodium molybdate.

4. The process of claim 1 where the oil is a recycle oil amount such that the molar ratio of water to carbon monoxide is from about 2:1 to 1:2, and ammonium molybdate, the weight ratio of oil to coal being about 2: 1 the amount of hydrogen being such that its partial pressure is about the same as that of said carbon monoxide, and the amount of ammonium molybdate being from by weight of said coal. 

1. THE PROCESS FOR DISSOLVING SUB-BITUMINOUS COAL WHICH COMPRISES HEATING AT ABOUT 400*C. TO ABOUT 425*C. UNDER A TOTAL PRESSURE OF FROM ABOUT 2000 TO ABOUT 5000 PSIG, A MIXTURE OF SAID FINELY DIVIDED COAL, A HYDROGEN DONOR OIL IN A WEIGHT RATIO TO SAID COAL OF FROM ABOUT 1:1 TO 5:1, CARBON MONOXIDE, HYDROGEN IN AN AMOUNT SUCH THAT ITS PARTIAL PRESSURE IS ABOUT THE SAME AS THAT OF SAID CARBON MONOXIDE, WATER IN AN AMOUNT SUCH THAT THE MOLAR RATIO OF WATER TO CARBON MONOXIDE IS FROM ABOUT 2:1 TO 1:2, AND AS A PROMOTER, AN ALKALI METAL OR AMMONIUM MOLYBDATE IN AN AMOUNT OF FROM ABOUT 0.5 TO ABOUT 10% BY WEIGHT OF SAID COAL.
 2. The process of claim 1 where the oil is anthracene oil and the promoter is an alkali metal molybdate.
 3. The process of claim 1 where the oil is a recycle oil and the promoter is sodium molybdate.
 4. The process of claim 1 where the oil is a recycle oil and the promoter is ammonium molybdate.
 5. The process of claim 1 where the CO and hydrogen are derived from producer gas.
 6. The process of dissolving sub-bituminous coal to form a liquid product similar to crude oil which comprises heating at a temperature of about 415*C. and at a total pressure of about 3000 psig, a mixture of said finely divided coal, anthracene oil, hydrogen and carbon monoxide obtained as producer gas, water in an amount such that the molar ratio of water to carbon monoxide is from about 2:1 to 1:2, and ammonium molybdate, the weight ratio of oil to coal being about 2:1, the amount of hydrogen being such that its partial pressure is about the same as that of said carbon monoxide, and the amount of ammonium molybdate being from about 1% to about 7% by weight of said coal. 